Vehicle hub unit

ABSTRACT

A vehicle hub unit includes: an outer ring; rolling elements; a hub wheel that is arranged radially inward of the outer ring via the rolling elements; and an inner ring member that is fixed to an end portion of a hub spindle of the hub wheel by clinching. A spline tooth portion that meshes with a tooth portion of a constant velocity joint that transmits driving force to the hub unit is formed at a clinched portion of the hub spindle. A protruding portion is formed at a radially inner side portion of a bottom of the spline tooth portion.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2010-192540 filed onAug. 30, 2010, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vehicle hub unit in which a member thatconstitutes an inner ring is fixed by clinching to an end portion of ahub spindle of a hub wheel to which a wheel is fitted.

2. Description of Related Art

A hub unit is used to support a wheel of an automobile such that thewheel is rotatable with respect to a suspension. FIG. 4 is a sectionalview that illustrates an example of an existing hub unit.

A hub unit 51 shown in FIG. 4 includes a hub wheel 53, an inner ringmember 54, an outer ring 55, and a plurality of rolling elements 56. Thehub wheel 53 has a hub spindle 52. The inner ring member 54 is fixed toone end of the hub spindle 52 by clinching. The outer ring 55 isarranged radially outward of the hub spindle 52. The rolling elements 56are rollably arranged between one of outer ring raceways 55 a of theinner peripheral surface of the outer ring 55, and an inner ring raceway52 a of the outer peripheral surface of the hub spindle 52 or an innerring raceway 54 a of the outer peripheral surface of the inner ringmember 54. A flange portion 57 is formed at an end portion (left endportion in FIG. 4) of the hub wheel 53, and a wheel of a tire, a brakedisc, and the like (not shown), are fitted to the flange portion 57. Afixing flange 58 is formed on the outer peripheral surface of the outerring 55. In addition, the fixing flange 58 is used to fit the hub unit51 to a vehicle body-side member (not shown) supported by a suspensionof a vehicle.

Rotational driving force of a drive shaft 60 is transmitted to the hubunit 51 via a constant velocity joint 59. As one method of transmittingthe rotational driving force, there is known a method in which, as shownin FIG. 5 in detail, a spline tooth portion (side face spline) 62 isformed at a clinched portion 61 of the hub spindle end portion forfixing the inner ring member 54, and then the spline tooth portion 62 ismeshed with a tooth portion (side face spline) 64 formed at an endsurface of the outer ring 63 of the constant velocity joint 59 (see, forexample, Published Japanese Translation of PCT Application No.2008-536737 and Japanese Patent Application Publication No.2008-174178).

In the hub units described in Published Japanese Translation of PCTApplication No. 2008-536737 and Japanese Patent Application PublicationNo. 2008-174178, rotational driving force is transmitted to the hub unitvia a constant velocity joint due to the mesh of the teeth that extendin a direction substantially perpendicular to a rotary shaft.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a vehicle hub unit to whichrotational driving force is transmitted via the above-described sideface spline, and in which stiffness of a spline tooth portion formed ata clinched portion of a hub spindle end portion is increased to therebymake it possible to increase an allowable loading torque for the hubunit.

An aspect of the invention relates to a vehicle hub unit including: anouter ring; rolling elements; a hub wheel that is arranged radiallyinward of the outer ring via the rolling elements; and an inner ringmember that is fixed to an end portion of a hub spindle of the hub wheelby clinching. A spline tooth portion that meshes with a tooth portion ofa constant velocity joint that transmits driving force to the hub unitis formed at a clinched portion of the hub spindle. A protruding portionis formed at a radially inner side portion of a bottom of the splinetooth portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a sectional view that illustrates a vehicle hub unit accordingto an embodiment of the invention;

FIG. 2 is an enlarged view that illustrates an end portion of a clinchedportion of the vehicle hub unit shown in FIG. 1;

FIG. 3A and FIG. 3B are views that illustrate a die for clinching an endportion of a hub spindle and for forming a spline tooth portion at theend portion;

FIG. 4 is a sectional view that illustrates an example of an existingvehicle hub unit; and

FIG. 5 is an enlarged view that illustrates an end portion of a clinchedportion of the vehicle hub unit shown in FIG. 4.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a vehicle hub unit according to an embodiment of theinvention will be described in detail with reference to the accompanyingdrawings. FIG. 1 is a sectional view that illustrates a vehicle hub unit1 according to the embodiment of the invention. FIG. 2 is an enlargedview that illustrates an end portion of a clinched portion of thevehicle hub unit shown in FIG. 1.

The vehicle hub unit 1 supports a wheel of an automobile such that thewheel is rotatable with respect to a suspension. The vehicle hub unit 1includes a hub wheel 3, an inner ring member 4, an outer ring 5 and aplurality of rolling elements 6. The hub wheel 3 has a cylindrical hubspindle 2. The inner ring member 4 is fixed to one end (right endportion in FIG. 1) of the hub spindle 2 by clinching. The outer ring 5is arranged radially outward of the hub spindle 2. The rolling elements6 each are rollably arranged between an outer ring raceway 5 a of theinner peripheral surface of the outer ring 5 and an inner ring raceway 2a of the outer peripheral surface of the hub spindle 2 or between anouter ring raceway 5 b of the inner peripheral surface of the outer ring5 and an inner ring raceway 4 a of the outer peripheral surface of aninner ring member 4. The rolling elements 6 are retained by a cage 20,and arranged at predetermined intervals in the circumferentialdirection. Seal members 21 are provided in an annular space formedbetween the outer ring 5 and the hub wheel 3. The seal members 21 closethe annular space from both ends of the annular space in the axialdirection.

A flange portion 7 is formed at the end portion (left end portion inFIG. 1) of the hub wheel 3. A wheel of a tire, a brake disc, and thelike (not shown), are fitted to the flange portion 7 with bolts. Afixing flange 8 is formed on the outer peripheral surface of the outerring 5. The fixing flange 8 is used to fit the hub unit 1 to a vehiclebody-side member (not shown) supported by the suspension of a vehicle.

The hub spindle 2 is a single-piece member that has a large-diameterportion 9 and a small-diameter portion 11. The large-diameter portion 9is formed at a position near the flange portion 7. The small-diameterportion 11 is smaller in diameter than the large-diameter portion 9, andis formed so as to be contiguous with the large-diameter portion 9 via astep 10. The inner ring raceway 2 a is formed in the outer peripheralsurface of the large-diameter portion 9. The inner ring raceway 2 acorresponds to the outer ring raceway 5 a of the outer ring 5.

The inner ring member 4 is fitted onto the outer peripheral surface ofthe small-diameter portion 11 of the hub spindle 2, and then an endportion of the small-diameter portion 11 is clinched to form a clinchedportion 12. In this way, the inner ring member 4 is fixed between thestep 10 and the clinched portion 12.

Driving force of a drive shaft 31 is transmitted to the hub unit 1 via aconstant velocity joint 30. The constant velocity joint 30 according tothe embodiment is a Birfield constant velocity joint. The constantvelocity joint 30 includes an inner ring 32, a plurality of balls 34 anda cage 35. The inner ring 32 is joined to one end of the drive shaft 31.An outer ring 33 is arranged radially outward of the inner ring 32. Theballs 34 are arranged between the inner ring 32 and the outer ring 33.The cage 35 retains the balls 34.

The outer ring 33 of the constant velocity joint 30 has a bowl-shapedouter ring cylindrical portion 33 a and an outer ring shaft portion 33b. The outer ring shaft portion 33 b extends from a center portion of anend surface of the outer ring cylindrical portion 33 a. The outer ringshaft portion 33 b has a hole 36 that extends in the axial direction.The inner peripheral surface of the outer ring shaft portion 33 b, whichdefines the hole 36, has an internal thread. The hub unit 1 is connectedto the constant velocity joint 30 by a cap bolt 38 that has an externalthread 37 at its end portion.

As shown in FIG. 2, a spline tooth portion 13 is formed at the endsurface of the clinched portion 12 of the end portion of the hub spindle2. A tooth portion 14 is formed at the end surface of the outer ringcylindrical portion 33 a, which faces the clinched portion 12. Owing tothe mesh of the spline tooth portion 13 and the tooth portion 14,rotational driving force of the drive shaft 31 is transmitted to the hubunit 1 via the constant velocity joint 30.

The number of teeth 13 a of the spline tooth portion 13 is 37, aprotruding portion 15 is formed at each bottom 13 b between theconsecutive teeth 13 a. Each protruding portion 15 protrudes toward thetooth portion 14 of the outer ring cylindrical portion 33 a that facesthe spline tooth portion 13. Each protruding portion 15 is formed at aradially inner portion of the bottom 13 b of the spline tooth portion13. More specifically, each protruding portion 15 is formed at thebottom 13 b at a portion substantially radially inward of a meshingportion 16 (hatched portion in FIG. 2) at which the tooth 13 a of thespline tooth portion 13 is in mesh with a tooth 14 a of the toothportion 14 of the outer ring cylindrical portion 33 a. By forming theprotruding portions 15, the stiffness of each of the teeth 13 a thatconstitute the spline tooth portion 13 is increased. Thus, the allowableloading torque for the hub unit 1 is increased. For example, theexperiment was conducted on the spline tooth portion having 37 teeth,and the maximum principal stress and the shear stress were respectivelyreduced by approximately 14% and approximately 24% in the case where theprotruding portions 15 are formed as compared with the case where noprotruding portions 15 are formed.

A predetermined clearance C1 is left between each bottom 13 b of thespline tooth portion 13, including the surface of the protruding portion15, and a top surface 14 c of the tooth 14 a of the tooth portion 14 ofthe outer ring cylindrical portion 33 a, which faces the bottom 13 b. Onthe other hand, a predetermined clearance C2 is left between a topsurface 13 e of each tooth 13 a of the spline tooth portion 13 and abottom 14 b of the tooth portion 14 of the outer ring cylindricalportion 33 a, which faces the top surface 13 e.

The spline tooth portion 13 is formed together with the clinched portion12 at the same time by fitting the inner ring member 4 onto the outerperipheral surface of the small-diameter portion 11 of the hub spindle 2and then subjecting the end portion of the small-diameter portion 11 toclosed die forging. In the present embodiment, a die 40 shown in FIG. 3is inserted into the opening of the hub wheel 3 at a portion to whichthe inner ring member 4 is fitted, and then the die 40 is oscillated ata predetermined inclination angle about an axis 40 a to perform ordinaryoscillating clinching. Through the oscillating clinching, the clinchedportion 12 and the spline tooth portion 13 are formed. At this time, arecess 41 having a shape corresponding to each protruding portion 15 ofthe spline tooth portion 13 is formed radially inward of each protrudingportion 40 b of the die 40, the protruding portion 40 b corresponding tothe bottom of the spline tooth portion 13. During closed die forging,the recesses 41 are used to form the protruding portions 15 of thespline tooth portion 13.

The tooth portion 14 of the outer ring cylindrical portion 33 a as wellas the spline tooth portion 13 is formed by closed die forging. Thepredetermined clearances C1 and C2 are set such that tolerances inclosed die forging are absorbed so as not to cause contact between theteeth when the constant velocity joint 30 is fitted to the hub unit 1.Although the clearances C1 and C2 vary depending on the accuracy ofclosed die forging, the clearances C1 and C2 are usually approximately0.5 to 1 mm.

In addition, a top surface 13 c 1 which is near the radially inner endportion and which is a part of the strip-shaped top surface 13 e of eachtooth 13 a of the spline tooth portion 13 is flush with a radially innerinclined surface 15 a of the corresponding protruding portion 15. Thus,it is possible to reduce concentration of stress to thereby enhance thestiffness of the teeth.

In addition, in the present embodiment, it is possible to enhance thestiffness of the teeth by forming the protruding portion 15 at eachbottom 13 b of the spline tooth portion 13, and, in addition, it ispossible to reduce stress loading on the die 40 by forming theprotruding portions 15. That is, in the embodiment shown in FIG. 1 andFIG. 2, spline formation is minimized to reduce the area of the flatportion of each bottom as compared with the existing example shown inFIG. 4 and FIG. 5. Therefore, it is possible to reduce a load on theprotruding portions 40 b of the die 40 accordingly. Specifically, a diepressing force required to form the spline tooth portion 13 is decreasedby approximately 20% to thereby make it possible to decrease stressloading on the die 40 (stress at the maximum stress portion) to a valueat or below half of the stress loading on the die 40 in the existingart.

The invention is not limited to the above-described embodiment, andvarious modifications and changes may be made within the scope of theappended claims. For example, in the above described embodiment, adouble row angular contact ball bearing is used as the bearing of thehub unit; instead, another bearing, such as a double row roller bearing,may be used.

In addition, in the above described embodiment, the number of teeth ofthe spline tooth portion is 37; instead, the number of teeth of thespline tooth portion may be other than 37 (for example, 31). Inaddition, in the above-described embodiment, the sectional shape of eachprotruding portion is a wavy shape. Alternatively, another sectionalshape, such as a semi-circular shape and a trapezoidal shape, may beemployed. In addition, in the above-described embodiment, there isemployed a third-generation structure in which an inner ring raceway isdirectly formed in the outer periphery of the hub spindle.Alternatively, a first-generation or second-generation structure inwhich a pair of inner rings is press-fitted onto a hub spindle may beemployed.

What is claimed is:
 1. A vehicle hub unit comprising: an outer ring;rolling elements; a hub wheel that is arranged radially inward of theouter ring via the rolling elements; an inner ring member that is fixedto an end portion of a hub spindle of the hub wheel by clinching; aspline tooth portion formed at a clinched portion of the hub spindle; ameshing portion at which the spline tooth portion meshes with a toothportion of a constant velocity joint that transmits driving force to thehub unit; and a protruding portion formed at a radially innermostportion of a bottom of the spline tooth portion, the bottom beingadjacent to the meshing portion, wherein the protruding portion projectsmore than the bottom and is formed radially inward of the meshingportion.
 2. The vehicle hub unit according to claim 1, wherein a heightof the protruding portion is set to such a height that a predeterminedclearance is left between the protruding portion and a top surface of atooth of the tooth portion of the constant velocity joint.
 3. Thevehicle hub unit according to claim 2, wherein the predeterminedclearance is 0.5 to 1 mm.
 4. The vehicle hub unit according to claim 3,wherein a portion of the top surface of the tooth of the spline toothportion, the portion being near a radially inner end portion, is flushwith a radially inner inclined surface of the protruding portion.
 5. Thevehicle hub unit according to claim 2, wherein a portion of the topsurface of the tooth of the spline tooth portion, the portion being neara radially inner end portion, is flush with a radially inner inclinedsurface of the protruding portion.
 6. The vehicle hub unit according toclaim 1, wherein a portion of the top surface of the tooth of the splinetooth portion, the portion being near a radially inner end portion, isflush with a radially inner inclined surface of the protruding portion.7. The vehicle hub unit according to claim 1, wherein the protrudingportion does not mesh with the tooth portion of the constant velocityjoint.